System for keying or modulating the radiation field of an antenna



Aprll 1958 s. L. STUTZ 2,831,188

SYSTEM FOR KEYING 0R MODULATING THE RADIATION FIELD OF AN ANTENNA N Filed April 8, 1955 2 Sheets-Sheet l INVENTOR. Sl/f/V S 72' l BY J/7- April 15, 1958 s. STUTZ 2,

SYSTEM FOR KEYING OR MODULATING THE RADIATION FIELD OF AN ANTENNA 2 Sheets-Sheet 2 Filed April 8, 1955 W4 W M 4 mm SYSTEM FOR KEYING R MODULATING THE RADIATION FIELD OF AN ANTENNA Sherla L. Stutz, Lewisburg, Ohio Application April 8, 1955, Serial No. 500,311

Claims. (Cl. 343-757) (Granted under Title 35, U. 5. Code 1952' sec. 266) modifying the radiation pattern of an antenna wherein the ground plane of the antenna is electrically changed to become more or less conducting and thereby alter the radiation pattern of the antenna.

It has long been known that the conductivity of the ground plane of an antenna is a contributing factor to the radiation pattern of the antenna. The present invention utilizes this fact in a novel method and means for eying or modulating the radiation pattern of an antenna. The basic method is applicable to any conventional type of antenna and has application to many different types of overall systems such as homing apparatus or other systems where lobe switching techniques or controlled radiation patterns are used.

It is an object of this invention to provide a method and means for altering the conductivity of the ground plane of an antenna at will to thereby change the radiation pattern and effectively key and/or modulate the antenna radiation pattern.

It is a further object of this invention to provide such a means which is of simple mechanical construction and which will hence result in maximum ruggedness and in a minimum of drag loss when used in aircraft installations.

These and other objects and advantages will be apparent to those skilled in the art from the following specification taken in conjunction with the attached drawings wherein:

Figure l is a cross sectional and partially schematic view showing an antenna and ground plane assembly having a slot therein.

Figure 2 is a plan view of the antenna and ground plane of Figure 1.

Figure 3 is an equivector plot of the radiation patterns resulting from the antenna of Figure 1 when the slot is short circuited and when the slot is open circuited.

Figure 4 is a plan view of an antenna and ground plane using a plurality of slots.

Figure 5 is a plan view of an antenna and ground plane assembly using a slot of a different shape from that in Figure 1.

Figure 6 is a diagrammatic view of a two slot single antenna system installed on aircraft with an equivector plot and graph of ti e resulting radiation pattern.

Referring now to the drawings, and in particular to Figures 1 and 2, an antenna 1, which may be any conventional antenna such as a half-wave horizontal or vertical antenna or which could be a slot or any type of stub antenna, has a conventional ground plane 2. The antenna coaxial feed conductor 3 is connected to the antenna and ground plane in a conventional manner as illustrated in Figure 1.

The ground plane 2 has a slot cut therein as shown at 2,331,188 Patented Apr. 15, 1958 in 4. Although the dimensions of the slot are not an absolutely critical factor, a'slot having a maximum dimension which is'less than one half a wavelength at the operating frequency is preferred. A switching means 5 is connected by lead 6 to one side of the slot and by lead 7 to the other side of the slot. The switch could be either mechanical or electronic but is shown in Figure 1 as comprising a coaxial system 5 which is shorted at one end it and which uses an electromagnetic ferrite material as a controlled variable dielectric. When coil 8 is energized from a source of signal 9 which may for example be a square wave source, the system offers a low impedance or attenuation between the sides of the slot and the slot is effectively short circuited. On the other hand, when coil 8 is deenergized the coaxial system offers a high impedance or attenuation and the slot is effectively open circuited. Of course, a control signal of a different form could be used to make the system act as a simple variable impedance to produce any desired time pattern of modulation, Such variable ferrite dielectric coaxial systems are commercially available and the switching means per se does not form a part of this invention. As noted above any suitable switch means may be used but the coaxial system described is preferred because of its simplicity, ruggednes, rapidity of operation and the ease with which its operation may be synchronized with other operating characteristics of any system with which the antenna may be used.

When the slot is open circuited, the slot effectively interrupts the current flowing in the section of ground plane in which the slot is located and thereby reduces the amount of energy in that part of the radiation pattern affected by that section of the ground plane. A typical resulting radiation pattern with the slot open circuited is shown in dashed lines in Figure 3. When the slot is short circuited, theslot no longer interrupts the current flowing in the ground plane and therefore increases the amount of energy in that part of the radiation pattern affected by that section of the ground plane. Effectively, short circuiting the slot nullifies the effect of its presence and a substantially symmetrical radiation pattern is obtained as shown in solid lines in Figure 3.

It will be apparent from Figure 3 that if the slot 4 is alternately open and short circuited an effect akin to that obtained with conventional lobe switching techniques may be obtained for direction finding, homing or other purposes at the points indicated by the vectors A and B. That is to say, only radiation received from the directions A or B will be received with equal magnitude in both conditions of the slot 4, hence an indication of direction is afforded. It will further be noted that the pattern produced by a single slot is substantially a cardioid giving maximum radiation in the direction indicated by the vector C. This fact alone may be used without switching simply to increase the directivity of an antenna or for direction finding, or systems could readily be devised which depend-upon an indication of the maximum difference in the radiations patterns obtained in the two conditions of the slot. It is obvious that such a system would have as its only ambiguity a degree difference which is easily resolved. Such systems are merely suggested by way of illustration and the details thereof do not of themselves form a part of this invention.

Figure 4 illustrates an antenna and ground plane system wherein four slots are symmetrically placed in the ground plane about the antenna. If these slots are sequentially open circuited, it is apparent that the effect will be to cause the vector C in Figure 3 to rotate. It should also be noted that optimum spacing and/or phasing relations between the antenna and slot of Figure 3 or slots of Figure 4, which slots may be either parasitically or directly phased, can result in a more highly directional pattern in thedirection C than that shown by way of example in Figure 3. This effect of rotation of vector C may be utilized for scanning or other purposes and it is obvious that any convenient number of slots may be used. Alternatively the plurality of slots may be used simply to provide separate modulation of each of the four quadrants of the radiation pattern.

The slot need not necessarily be: of the rectangular shape shown in Figures 1 to 4. Figure 5 illustrates by way of example an alternative shape of slot 4', which has been found to be useful. Of course, a change in the shape of the slot will change the resulting radiation pattern which thus affords a means of designing a radiation pattern which is optimum for the intended application. In general the shape, position and phasing of the slot or slots may be varied as design parameters to obtain a desired impedance, bandwidth, and radiation pattern.

It should be noted that all of the necessary components of the system are simple, rugged and durable and that no moving parts are used. When used with airborne applications the ground plane is frequently a part of the skin of the aircraft and the present modulation system does not add any protruding parts which would increase the drag on the aircraft. If the modulating slot is used with a slot antenna or radiator, no protruding parts whatsoever are necessary.

Figure 6 is a diagrammatic view showing an antenna 1 and two slots 4;: and 4b installed on an aircraft P. Slots 4a and 4b are alternately and oppositely open and short circuited by switching means of the type shown in Figure 1. When slot 4a is open circuited the antenna has the radiation patterns indicated by I whereas when slot 412 is open circuited the antenna has the radiation pattern indicated at II. The graphs at the right of Figure 6 show a time plot of the voltage E which would be induced in antenna 1 by equal signal sources located at direction D, H, and G respectively, these directions being indicated by the corresponding vectors on the radiation plot. The graph would, of course, also indicate the relative signal strength transmitted in each of these directions from the same antenna since it is well known that a given antenna has the same characteristics for transmission that it has for reception.

It is apparent that the direction HH, determined by the intersection of the two radiation patterns is the only direction in which equal signal will exist regardless of which of the slots 40 or 4b is open circuited. Deviations from equality for directions D and G, for example are shown on the graph and are of course determined by the intersection of the vectors D and G'in these directions with the radiation patterns I and H.

Thus it is apparent that the directional equi-signal response of this improved and simplified antenna installation may be used with any conventional homing equipment with which the plane may be equipped. Although the slot technique may be used with any conventional antenna, it is particularly advantageous in airborne applications to use the ground plane slots in conjunction with a slot antenna so that the entire system offers zero drag to the aircraft.

While a specific embodiment of the invention has been described in detail by way of illustration, it is understood that the invention is defined solely by the appended claims and embraces any embodiment falling within the terms and spirit thereof.

What I claim is:

1. An antenna system comprising, an antenna, a ground plane for said antenna, circuit means to conduct energy to and from said ground plane and said antenna,

said ground plane consisting of an electrically conducting solid material, and slot means in said ground plane in spaced relation to said antenna to interrupt the current flow in a portion of said ground plane.

2. Apparatus as in claim 1 wherein the axis of said antenna is perpendicular to said ground plane.

3. Apparatus as in claim 1 wherein a variable impedance means is connected across said slot means.

4. Apparatus as in claim 1 wherein a switching means is connected across said slot means, said switching means being connected to open circuit said slot means in one condition and to short circuit said slot means in another condition of said switching means.

5. Apparatus as in claim 4 wherein said switching means comprises a coaxial system having ferrite material as a controlled variable dielectric and a coil associated with said coaxial system in such a manner that the energization and de-energization of said coil varies the impedance of said coaxial system, and means to apply a control signal to said coil.

6. An antenna system comprising, an antenna, a ground plane for said antenna, means to conduct energy to and from said ground plane and said antenna, said ground plane consisting of an electrically conducting solid material, and a plurality of slots in said ground plane in spaced relation to said antenna, said slots being arranged symmetrically with respect to said antenna.

7. In combination with an aircraft, a slot antenna, an electrically conducting ground plane surrounding said slot antenna, circuit means to conduct energy to and from said antenna and said ground plane, a plurality of slots in said ground plane in spaced relation to said antenna, and switching means connected across each of said ground plane slots, each said switching means being so connected that said slot is open circuited in one condition of said switching means and short circuited in another condition of said switching means.

8. A controlled pattern antenna system comprising an antenna ground plane of conducting material, an antenna mounted in said ground plane, a coaxial conductor connected to said antenna and said ground plane, and means independent of said antenna operable to vary the attenuation characteristic of a portion of said ground plane.

9. A controlled pattern antenna system comprising an antenna ground plane of conducting material, an antenna mounted in said ground plane, a coaxial conductor connected to said antenna and said ground plane, said ground plane having a slot therein in spaced relation to said antenna, and switching means operable to vary the attenuation across said slot.

10. A controlled pattern antenna system comprising an antenna ground plane of conducting material, an antenna mounted in said ground plane, a coaxial conductor connected to said antenna and said ground plane, said ground plane having a slot therein in spaced relation to said antenna, and switching means operable to vary the attenuation across said slot, said slot being positioned transverse to a line between said antenna and said slot, said slot having a length of less than one half wave length of the operating frequency of the system.

References Cited in the file of this patent UNITED STATES PATENTS 2,507,528 Kandoian May 16, 1950 2,555,443 Harvey June 5, 1951 2,632,851 Lees et al Mar. 24, 1953 FOREIGN PATENTS 653,018 Great Britain May 9, 1951 

